Here is a link to the "Annual Statistical Report on the Social Security Disability Insurance Program, 2009". This report provides a wealth of statistical information on the Social Security Disability program.
http://www.ssa.gov/policy/docs/statcomps/di_asr/2009/index.html
Highlights
Size and Scope of the Social Security Disability Program
* Disability benefits were paid to over 8.9 million people.
* Awards to disabled workers (970,696) accounted for over 89 percent of awards to all disabled beneficiaries (1,081,983).
* In December, payments to disabled beneficiaries totaled about $9.1 billion.
* Benefits were terminated for 630,074 disabled workers.
* Supplemental Security Income payments were another source of income for about 1 out of 6 disabled beneficiaries.
Profile of Disabled-Worker Beneficiaries
* Workers accounted for the largest share of disabled beneficiaries (87 percent).
* Average age was about 53.
* Men represented nearly 53 percent.
* Mental disorders was the diagnosis for about a third.
* Average monthly benefit received was $1,064.30.
* Supplemental Security Income payments were another source of income for about 1 out of 8.